Saturn's hexagon's mystery solved

Researchers have now been able to study and measure Saturn's hexagon and also establish its rotation period.

They also suggest that the period could be the same as that of the planet itself.

In 1980 and 1981 NASA's Voyager 1 and 2 space probes passed for the first time over the planet Saturn, located 1,500 million km from the Sun. Among their numerous discoveries they observed a strange, hexagon-shaped structure in the planet's uppermost clouds surrounding its north pole.

The hexagon remained virtually static, without moving, vis-a-vis the planet's overall rotation that was not accurately known. What is more, the images captured by the Voyager probes found that the clouds were moving rapidly inside the hexagon in an enclosed jet stream and were being dragged by winds travelling at over 400 km/h.

After measuring the positions of the hexagon vertices with great precision, researchers in the UPV/EHU's Planetary Sciences Group, in collaboration with astronomers from various countries, determined that its movement remains extremely stable, and on the basis of the cloud movements, that the jet stream inside it remains unchanged. For this study the researchers used images taken from the Earth between 2008 and 2014.

Due to the tilt of approximately 27 degree of the planet Saturn, its polar atmosphere undergoes intense seasonable variations with long polar nights lasting over seven years, followed by a long period of 23 years of variable illumination.

The UPV/EHU researchers suggest that the hexagon and its stream are the manifestation of a "Rossby wave" similar to those that form in the mid-latitudes of the Earth.

On Saturn, a hydrogen gas planet, ten times the size of the Earth, cold in its upper clouds, without a solid surface, and with an atmosphere as deep as that of an ocean, "the hexagonal wavy motion of the jet stream is expected to be propagated vertically and reveal to us aspects of the planet's hidden atmosphere," pointed out Agustin Sanchez-Lavega, Head of the Planetary Sciences research group.

The research has been published in the journal Geophysical Research Letters.